In recent years, electronic devices such as digital cameras, smart phones and tablets have become popular, and a demand for compact camera modules has been increased. For these camera modules, plastic lenses are preferably used, rather than glass lenses. This is because a plastic lens can be used in various forms such as a thin lens or an aspherical lens, and the plastic lens is inexpensive and the mass production thereof is easily carried out by injection molding.
For optical lenses, resins having various structures, which are to be replaced for glass, have been developed, and various monomers have been studied as raw materials therefor. Among optical transparent resins, an optical lens consisting of a thermoplastic transparent resin is advantageous in that it can be produced in a large amount by injection molding, and further in that the production of an aspherical lens is easy, and thus, it is presently used as a lens for cameras. As such an optical transparent resin, for example, polycarbonate consisting of bisphenol A (BPA) had been mainly used, but thereafter, polymers having a fluorene skeleton such as 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene (BPEF) (Patent Literatures 1 and 2) have been developed. Moreover, as a material having a high refractive index and low birefringence, a resin comprising, as a raw material monomer, a dihydroxy compound having a binaphthalene skeleton has been developed by the present inventors (Patent Literature 3).
Such a resin comprising, as a raw material monomer, a dihydroxy compound having a binaphthalene skeleton is preferable as an optical material, but the resin is problematic in that it has a high saturated water absorption rate and a dimensional change easily occurs upon molding. In addition, if such a saturated water absorption rate is high, a long drying time becomes necessary upon molding, and it may cause coloration. Accordingly, it has been desired to develop a resin that is useful as an optical material and has a low saturated water absorption rate.